PA: Best way to create reminders (notifications)

Hi all.

Ok, this is kind of open ended question. I´m looking at Contracts (yes, the one with R in it , btw it would simplify if Sugar just called it Agreements even though there is a technical difference...). There we have the field "Expiration Notice" (date and time). Good stuff. But what if I wanted to build a process that would, at the time of "Expiration Notice":

a) Change the status from X to Y

b) Assign the contract to team A

c) Some other stuff

Basically, when expiration notice date comes, a process starts. I understand that having all my 800 contracts constantly in PA processes is not very economical & handy so I am trying to figure out another way to trigger the process.

What do you guys suggest as ways to do that?

This is similar to my PA: Date field is after another date field  thought but not quite because that thought requires each Contract to be in a process comparing dates.

Thanks guys

KGM

Ent. 7.7.0.0.